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' es ss INVENTOR PHILIP o. nomzvrv ATTORNEY United States Q STATIC INVERTER Philip D. Corey, Waynesboro, Va., assignor to General Electric Company, a corporation of New York Filed June 8, 1962, Ser. No. 200,986 17 Claims. (Cl. 321-45) This invention relates to inverter circuits. More particularly, it relates to inverter circuits for converting direct current power to alternating current power employing gate controlled rectifiers as switching elements.

Heretofore, in the operation of DC to AC inverter circuits employing gate controlled rectifiers, a major problem has been encountered when, at the end ofa half cycle of operation, it is desired to render the conductive gate controlled rectifier 'nonconductive, and to render a complementary gate controlled rectifier conductive to initiate the next cycle of opposite polarity conduction. This changing of conductivity from one switchof an inverter is commonly referred to as comcalled auto-impulse type wherein the operation of rendering conductive the nonconductive gate controlled rectifier initiates commutation. This type of inverter circuit presents the advantage in that a minimum number of controlled rectifiers are required, i.e., with auto-impulse type commutation, the controlled rectifiers are utilized to handle the load current as well as to initiate commutation. Such inverter circuits are readily contrasted with inverter circuits wherein auxiliary switching devices are utilized solely to enable commutation of the separate power handling gate controlled rectifiers. v I

For power inverter circuits to be effective in operation,

.they have major requirements such as the ability to drive reactive loads and to operate under no load conditions. Many known circuits have this ability. Also, in such known circuits, the commutating capacitor may be relatively small since the capacitance value of the capacitor depends upon the maximum amount of current to be commutated and does not have the function of correcting for reactive load current.

A persistent problem which still exists with these latter known circuitsresults from the fact that currents of high RMS value are forced to flow through an output transformer and the DC power'source during the commutation intervals. This is, of course, highly undersirable since such output transformer consequently has to be quite large to avoid its being overheated. Also, depending upon the impedance of the DC power source, appreciable ripple is induced on the DC supply voltage when these RMS currents fiow through the source.

It is, accordingly, an important object of thisinvention to provide an inverter circuit of the auto-impulse" type which has the ability to drive reactive loads, which can operate at no load conditions, which permits the. comm'utating capacitor to be small and in which, the high RMScommutation currents do not fiow in the output transformer or in the DC power source thereby allowing the use of an output transformer of substantially minimum size and weight and whereby substantially minimum ripple is induced on the DC supply voltage.

It is another object to provide an inverter in accord and light weight.

atent 1 Patented Dec. 17, 1968 Generally speaking and in accordance with the invention, there is provided a circuit for converting the output from a DC source to an AC power output comprising a a second series arrangement of a second and comple- *mentary gate controlled rectifier connected across the source, the first and second elements presenting a low impedance when their respectively series associated gate". 2

controlled rectifiers are conductive and presenting a high impedance when their respectively series associated gatecontrolled rectifiers are nonconductive. Acommutating capacitor is included connected across the gate controlled rectifiers. Signal generating means is provided in circuit with the gate controlled rectifiers for alternately gating into conductivity the gate controlled rectifiers during suc-' cessive half cycles of output from the signal generating means, the capacitor charging in a polarity during the con: ductive period of one of the gate controlled rectifiers such as to apply reverse voltage thereto and render it nonconductive when the other of the gate controlled rectifiers is rendered conductive by the signal generating means, the element in series with the other gate controlled rectifier presenting a high impedance when the other gate controlled rectifier is rendered conductive.

The novel features, which are believed to be characteristic of the invention, are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of'operation together with further'objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings.

In the drawings, FIG. 1 is a schematic representation of a first illustrative embodiment of a center tapped inverter circuit in accordance with the principles of the invention;

FIG. 2 is a schematic depiction of a circuit'similar to FIG. 1; I

FIG. 3 is a schematic diagram of a circuit similar to the circuits of FIGS. 1 and 2;

FIG. 4 is a schematic representation of a circuit similar I to that of FIGS. 1 to 3;

FIGS. 5 to 10 are schematic diagrams substantially the same as the diagram of FIG. 4 and are conveniently utilized in the explanation of the operation of the circuit 1 of FIG. 4; and

FIG. 11 is a schematic depiction of a bridge type inverter circuit in accordance with the principles of the invention.

Referring now to FIG. 1 wherein there is shown a center-tapped (or parallel") type inverter circuit, a first silicon controlled rectifier 10 has its anode connected to the positive terminal 11 of a DC power source (not shown) through the low resistance winding 14 of a first saturable reactor 12 and half 19 of the primary winding 20 of a center-tapped output transformer 18. Similarly, a second silicon controlled rectifier 24 has its anode con-' nected to positive terminal 11 through the low resistance winding 30 of a second saturable reactor 26 and the other half 21 'of primary winding .20. The cathodes of silicon controlled rectifiers 10 and 24 are-connected to the negative terminal 13 of the DC source.

Connected between the respective gate electrodsof silicon controlled rectifiers 10 and 24 is the series arrangement of a current limiting resistor 32, the secondary winding 36 of a transformer 34, across which there is developed the output of a saturable gating source 38,

such as a rectangular wave multivibrator, and a current limiting resistor 40. For controlling the voltage applied to the gate electrodes of the silicon controlled rectifiers,

.between negative terminal 1 sistor 32 and winding 36 and the anode to cathode path 13 and the junction 33 of reof a seconddiode 44 is interposed between negative terrninal 13 and'the junction 37 of winding 36 and resistor 40. 1 Provided between negative terminal 13 and the junction '15 of primary winding half 19 and reactor winding 14 is the anode to cathode path of a pump-back diode 46' and provided between negative terminal 13 and the unetion 29 ofprimary winding half 21 and reactor Winding 30 is the anode to cathode path of a pump-back diode 48. A commutating capacitor 50 is connected between the anodes of silicon controlled rectifiers l and 24. A reset current path for saturable reactors 12 and 26 -is provided by the series arrangement of a low power winding 16 for saturable reactor 12 connectedto junction 15, a current limiting resistor-52 and the low power'winding 28 for saturable reactor 26 connected to junction 29.

. Saturahle reactors 12 and 26 aresuitably fairly small reactors. The characteristics of reactors 12 and 26. are so chosen such that the product of-the turns of the low resistancc winding suchas'winding 14 of reactor 12, the core ,thesupplying of load current during the short commutation interval and does not have to be of alarge enough value for lagging reactive load current.

It is to be noted that the energy stored in capacitor" 50 and not needed to supply the load-during thejresonant discharge is returned to capacitor 50 during the resonant discharge. This current pulse does not flow through the windings of output transformer 18 -or back to the DC.

, power supply. Also, since the flux direction in the core of area and the core saturation flux density enables the core tion during the brief commutation interval, and the configuration of the reactor is such that its after-saturation in:

ductance is of a suitable 'value to form a series tuned LC circuit with commutating capacitor 50. To provide reactors which have the aforesaid characteristics, the windings of reactors 12 andi26 can be wound around two cores. instead of the usual single core, one core beingof asquare hysteresis loop type material to produce the linear inductors such as inductors 54, 56, 58, 60 and 62 shown in dotted outline in FIG. 1 may be utilized. 7

I In; considering the operation of the circuit of FIG.'1. letit be assurne'd. that silicon controlled rectifier is gated into conductivity by a pulse from gating source 38. Due to auto-transformer action, i.e., the transformer "action between the two'halves of primary winding 20,

essentially twice the voltage from the DC source is established across primary winding 20 with the positive termi nal being at the designating polarity dot end of the winding. Also, capacitor 50. in this situation, charges to twice the voltagcfrom the DC source with the polarity as shown in FIG. 1. This polarity condition of primary winding 20 causes saturable reactor 26 to be reset as shown by the designating polarity'dot thereon by reset current flowing fromiunction 29 to junction 15 through reset winding I .28, reset resistor 52, and reset winding 16.

When silicon-controlled rectifier 24 is gated into conductivityby the next half cycle of output from gating source 38, arld .gating' voltage is removed from silicon.

K controlled rectifier 10, commutating capacitor 50 eifec tively is connected directly across silicon controlled rectifier. 10in a polarity such as to apply reverse voltage thereto and to by-pass the load current. Capacitor 50 resonates with the after-saturation inductance of winding 14 of'saturable reactor 12, the natural frequency of this of the reactor to go from fnegative to positive saturadesired .tums area-fiux density product:and the second core suitablylconsisting ofa material suchas powdered permalloy to enable the providing'of the desired aftersaturation inductance. Instead ,of utilizing such double core reactors to insure proper after-saturation inductance.

I ssturable reactor '26is proceeding from negative to positive saturation, winding 30 of saturable reactor 26 presents a relatively high impedance during the commutation negative and reactor 12 is reset commutation pulse.

I It has been found in the circuit of FIG. .1 that there exists'therein'a "ferrorcsonant" oscillation in the LC circuits formedby commutation capacitor 50 and the saturable reactors l2 and 26. A term-resonant oscillation occurs in an LC circuit. wherein a non-linear in- Y ductor, i.e., one having a saturable core is utilized. In this .type of circuit, when the core of the inductor saturates,"

it abruptly' goes from a high impedance to'a 'low impedance? state and rapidly transfers its energy tojthecapacitor. Accordingly, in such oscillation, capacitor 50 actually overcharges to more than twice the value of- "the DC power source. To suppress this oscillation, several circuit modifications can be made .in the circuit of FIG. 1-. Thus, for 'e xampleJhe value of reset resistor'52 can be reduced to the point: that theoscillation of the I aforesaid LC circuits is effectively damped. The ferroresonant" oscillation canalso be damped with the ar-- 'rangement of FIG. 2. it is seen in the latter circuit'that it is essentially the same as'the circuit in-FIG. 1 except that the anode to cathode paths of diodes 64 and 66 are interposed between the windings 14 and 30 and the anodes of silicon controlled rectifiers 10 and 24 respectively. In the circuit of FIG. 2 in the event that resistor 52 does not provide sufficient damping for the suppression of this "ferro-resonant oscillation, then diodes 64 and 66 function effectively as clamps to, provide the required damping effect. I I

It has been found that advantage can be taken of this ferrorcsonant" oscillation tendency. In FIG. 3, there is" shown a circuit in which this advantage is availed of.

It is noted that the circuit of FIG; 3 is essentially similar to thecircuit of FIG. 1. However, in the circuit of FIG.

1 3. saturable'reactors 12 and 26 are shown having only series LC combination controlling the duration of time ,for silicon controlled rectifier. 10 to be reverse-biased (commutation time). The current associated with this gresonantdischarge'fiows out of side 51 of capacitor 50, I through silicon controlled rectifier 24, diode 46, winding 14 of sat'ura'ble reactor; 12, andback to side 53=of capacitor 50. This resonant effect tends-to maintain thc' com'.

mutation time fixed for variations of the inyert'cr' load from zero load to rated load. Hence,- thcQLC circuit is dcsigned to provide reverse voltage for a'pcriod suflicient-ly'long' to enable the silicon controlled :recti'fiers to regain their'tlorward blocking. ability. The capacitance value-ofcapacitor.Stineedpnly be large enough tocnable.

one winding and not having a reset winding. During the period of the commutation pulse in the operation of the circuit of FIG. 3, capacitor 50 actually over-charges" to more than twice the voltage from the DC source due to this ferroresonant oscillation action. In the circuit of FIG. 3, as capacitor 50 discharges back to a value of twice the DC source voltage. a saturable reactor is reset without the necessity of added reset windings. The values of resistors 68 and 70 are so chosen that further ferroreson'ant'oscillation is effectivelydamped out.

In FIG. '4, there is shown a' circuit in accordance'with the invention wherein the design of saturable. reactors 12 and 26 is considerably simplified. The desired'requirements'oflsaturable reactors that have to be met simpltaneousl'y are adequate volt-secondholdlotr' capability and 9 sufficient"after-saturation inductance to enable their resonating with commutating capacitor 50. In the circuit of FIG. 4, winding 72, for-example. of saturable reactor-12 is designed to provide the desired volt-second hold' 'ofl capability. Since, in many practical .d'es-ign situations, it

may-,happen'that theiaftensaturation inductance of Wind ing 72 is somewhat difi'erent from the desired optimum value, winding 74 is added to the saturable reactor. In this connection, it is to be noted that winding 74, connected inseries arrangement with winding 72, is part of the series resonant circuit with the commutating capacitor '50 during the commutating interval. Accordingly, winding 74 can be chosen independently sothat'the aftersaturation inductance of saturable reactor 12, for example, i.e.,

- the after-saturation inductance of the combination of windings such as windings 72 and 74 is of the desired value.

In this connection, winding 74 may be chosen to either increase or decrease the after-saturation inductance of the saturable reactor depending upon the polarity of winding connections. I

To reset the saturable reactors such as, for example, saturable reactor 12, many arrangements may be utilized. Thus, for example, an additional winding 76 and resistor 78 shown in dotted outline may be connected as depicted with or without diodes 64 .and 66, also shown in dotted outline for suppressing ferroresonant oscillation. Al-

N ternatively, winding 76 may be omitted and resistors 68 and 70 may be inserted as shown to take advantage of the ferroresonant condition to provide the resetting action in the same manner as with circuit of FIG. 3. FIGS. 5-10 which are essentially drawings of the circuit of FIG. 5 which includes resistors 68 and 70 are included previously described in connection to clarify the operation of the commutation circuit showntherein utilizing commutation reactors in accordance with the invention. Thus, FIG. 5 shows the condition which obtains at the end of a'half cycle of operation. It is seen thzit load current i, is flowing "as shown therein through silicon controlled rectifier and commutating capacitor 50 is charged as depicted. Itis assumed that the circuit inductances are of a value suflicient such that load current continues in the same direction during the verybrief commutating intervals until the next half cycle ofoperation is initiated by gating silicon controlled rectifier 24 into conductivity and removing the gating voltage from silicon controlled rectifier 10.

' FIG. 6 shows the situation that obtains immediately following-the gating of siliconcontrolled rectifier 24 into conductivity. Silicon controlled rectifier 10 is switched to its blocking slate by the polarity ofthecharge on capacitor 50' and a resonant discharge is occurring, in which the excess energy on capacitor 50, not needed to supply the load, is first stored in the after-saturation inductance. of saturation reactor IZJCommutating current plus load current flows through silicon controlled rectifier 24. Saturable 'reactor 26. which was previously completely reset, is now proceeding toward saturation due to the influence of the voltage applied to winding 80, saturable reactor 26, of

course. presenting a relatively high impedance during this commutating interval. commutating current, i persists until the energy in capacitor 50 has been transferred into saturable reactor 12 and from saturable reactor 12 back into capacitor 50, thereby charging capacitor'50 to the opposite polarity.

Substantially simultaneously with the cessation of the flow of commutating current i saturable reactor 26' saturates and presents essentially zero impedance. The situation depicted in FIG. 7 now exists. Load current i, flows through pump-back diode 48, winding 82 of the now saturated saturable reactor 26 "and output transformer 18, thereby returning energy from the load to the DC power source.

It is to be noted as shown in FIG. 8 that the terminal voltage of the primary winding of transformer 18 have suddenly reversed, thereby applying a voltage across winding 72 of saturable reactor 12, this voltage being I g the difference between the voltage across capacitor and the terminals of primary winding 20. This condition charging of capacitor 50 to a voltage higher than the transformer terminal voltage.

In FIG. 9 there is shown the condition at the end of this over-charging. It is to be noted that the difference between the voltages across capacitor 50 and the transformer terminal voltage is applied across winding 72 of saturable reactor 12 to eifect the resetting of saturable reactor 12. Resistors 68 and 70 are chosen to have a value respectively such as to damp out any further oscil- .lations between the saturable reactors and capacitor 50,

thus leaving saturable reactor 12 in the reset condition and in a ready state for the alternate commutation impulse.

In FIG. 10 there is shown the circuit condition after the commutation has been completed. Thus, it is seen that while the half cycle proceeds, current i, reverses as energy is returned from the DC source to the load and the condition of the circuit is comparable to the condition depicted in FIG. 6 with silicon controlled rectifier 24 conducting instead of silicon controlled rectifier 10 and with polarities reversed.

In FIG. 11 there is shown an arrangement, for example, where saturable reactor commutation is utilized in a bridge type inverter circuit. The gating source 88, although shown in four locations, may be a single common source. In this circuit, silicon controlled rec- 1 tifiers and 96 are simultaneously gated into conductivity by a half cycle from the output of gating source 88 and during the other half cycleof output from gating source 88, silicon controlled rectifiers 92 and 94 are.

triggered into conductivity. Capacitor98 functions to' provide commutation between silicon controlled rectifiers 90 and 92 and capacitor 99 functions to provide commutation between silicon controlled rectifiers 94 and 96. In this manner, the alternating current voltage is applied to load 100. Diodes 102, 104,106 and 108 function-t0 provide pump-back paths for handling reactive loads andv also function in the commutation circuits in the same manner as they do in the center-tapped circuits depicted in FIGS. 1-4. Saturable reactors 110, 112, 114'and 116 perform the decoupling and resonant commutating with capacitors 98 and'99 respectively and resistors 118, 120, 122 and 124 serve to damp ferroresonant type oscillations while permitting the proper reset voltages to beapplied to the saturable reactors. Similar to many variations that may be utilized in the center-tapped inverter circuits, linear reactors and/or additional windings on the saturable reactors may be utilized in the bridge inverter circuit of FIG. ll.- v

In connection with the design of saturable reactors to I function as the volt-second gate commutating reactors in causes a relatively small transient current component in FIG. 8. This transient current component is shown as i, the transient component rcsulting in a resonantly over- FIGS. I-4 and FIG. 11, it is assumed that the static inverter VA output is held constant and that the DC I I supply voltage is the independent variable.

With regard to inductance, as voltage is increased, cur-. rent reduces linearly, thereby keeping the static inverter,

age. In the series LC resonant circuit which includes the after-saturation inductance of the primary winding of the saturable reactor, the peak current is given by the expression 1,,: doubled, peak commutating capacitor capacitance is one-fourth of the C,,,. Thus, as the .supply voltage is original capacitor value to maintain constant commuta-- tion time. Keeping the LC product constant, there is needed four times the original inductance L. This is exactly what is available since the voltage is doubled,

current is halved and the required "saturable reactor is also doubled, and, thus, there isob- V to behandled will vary as-follows;

g seen that no change inthe SillulablfimfiCtOI primary mutating capacitor hasto be charged through-transformer I grnerit ofafter-saturation inductance.

the amount of turns-on the primary 'windings of the stained four times the value of the original inductance L. r JWith regard tothe power losses in the saturable 'r'eactor, there are to-be considered thecopper losses, the 5 power losses, andth'e core losses. In connection with the copper losses in thenprimary winding of the saturable vreactor, the primary winding RMSjcurrents which have The currents, both.comniutating'and steady-state,"

- vary inversely with the operating voltage -of the inverter. "The power loss varies as the square of the currents, and

' -for a given resistance, tends to vary inversely as the 1 1 square of the supply voltage. In contrast, as' the supply proportion and the-resistance of the windings vary as i 1 th'e squareof the. number of turns if the winding volume '1 is'maintained at a constant value. Thus, for a given v volume, the saturable reactor winding resistances vary as the square of the supply voltage-It. is; accordingly,

winding copper losses occurswhen the operating volt- 'age of the inverter is varied. I ,In connection with the power losses, where a separate commutating circuit may appear as a load to the resetting circuit. *In a given time interval, depending upon inverter operating frequency, the voltage on- 'the com- I action upto a voltage proportional totheinverter supply voltage. Since n .v Ae,,= f 1,1113 ,enprsses, voltage change on the commutating capacitor due to reset current, .it is noted that the reset winding current is proportional to the commutating capacitor C i 5 Y and the change in capacitor voltage, Ale Since G varies inversely as the square of the applied, voltage, and A2,,

varies directly with supply voltage, reset winding current 4 varies inversely with supply'voltagelt is, therefore, seen that because of the manner in whichwinding resistances vary for constant winding volume, changes in supply voltage do not result in any change in Jreset windingcopper loss. 1 I With regard to core losses, core loss is not a function 0f the inverter supply voltage butis. a function of the rate of change of flux and the required commutations I per secondwhich in turn depend upon the inverter fre- "quency. If the commutation interval is maintained constant,-rate"of change of flux densityis constant. Thus, for

a given inverter frequency, the core loss in the s'aturable ,reactor is independenti'of operating voltage. Froni the i, foregoing it is seen that if the static inverter VA output I is keptconstant, changing the DC supply voltage. does not'result in'changing the physical size-of the saturable v reactor. Also, if the saturable reactor is designed to have n the proper after-saturation inductance at one voltage level, as the supply voltage value is changed, the saturable reactor will naturally have the desired aftersaturation inductance whichis required. This is, of course, true for the case where a powdered iron core is included in the windings of the saturable reactors to permit adjusts =While: there have been shown particular embodiments 5 of this invention, it'will, of course, be understood that it is not intended to be limited thereto since manymodifications both in the circuit arrangements and in the instrumentalities employed therein may be made and it is therefore contemplated by the appended claims to cover '7 l any such modifications as fall within the true spirit and n scopeof theinvention. v V

What is claimed as new and desired to he secured by Letters Patent of the United States is:

1 Acircuit for converting output from a DC hected across said source, said first and second saturable senting a high impedance when said other gate controlled- ,rectifier is initially gatedinto conductivity.

g V source to an AC power output comprisinga first series 1' I 1 w nding s ut lized to reset the saturable reactor, the 25 ing a second gate controlled rectifier and a second satu' rable reactor, a transformer connected between saidcharging in a polarity during the conductive period of 5 ahigh impedance when said other gate controlled rectiher is initiallygated into conductivity to prevent said arrangement of *a first gate controlled rectifier and a first; saturable device connected across said source, a second series arrangement-of a second and complementary gate controlled rectifier and asecond saturable device condevices respectively presenting a' low impedance when; said first and second gate controlled re'ctificrs are corre-I spondingly respectively conductive, a commutating capaci tance connected between said gate controlled rectifiers, and signal generating means in circuit with 'saidgate,

.controlled rectifiers for alternately gating into conduc- 'tivity said gate .controlledrectifiers during succcssive half- [cycles of output from said signal generating means, said i ivoltage isincreased, more turns are required in direct 1 capacitance. charging in a polarity. during the conductive 7 period .of one of said gate controlled rectifiers such as to apply reverse voltage thereto to render it nonconductive ,svhen the other-of said lgate controlled rectifiers'is gated into conductivity, the 'saturable device in series 1 arrangement with said other gate controlled rectifier pre-I 2. A circuit for converting the output-from a-DC arrangement of a first gate controlled rectifier and a first, saturable reactor, a second series arrangement compris-f arrangements, said combination of said'series arrange ments and said transformer being connected acrosssaid source, said first and second saturable reactors respec- 5 tively presentinga low impedance when, said first and second gate controlledrectifiersare respectively corref spondingly conductive, a commutating capacitance con-J nected between said gate controlled rectifiers, and signal 1 generating means in circuit with said gate controlled rec- I tifiers for alternately gating intoconductivit'y said gate! controlled rectifiers during successive half cycles of output from said signal generating means, said capacitance one of said gate controlled rectifiers such as to apply reverse'voltage thereto to render itnonconductive when 1 the other ofs aid gate controlled rectifiers is initially gated into conductivity, the saturable reactor in series arrangement with said other gate controlled rectifier presenting capacitor from discharging transformer. i I

3.,A circuit for converting the output from a DC source to an AC power output comprising first and sec-.. 1

into said source and said f 1 'ond sam able reactorsea h of said saturablc Ieactors comprising a low resistance winding and a low power winding, first and second gate controlled rectifiers in first 3 v 5 ,and second series arrangementswith saidfirst and second i low resistance windings respectively, a transformerconv,

- nccted between said arrangements, said combination of said series arrangements and said transformer being connected across said source, said first and second saturable reactors presenting a low impedance when said first and l second gate controlled rectifiers are respectively correspondingly conductive, a commutating capacitance CD11". J nected between said gate controlled 'rectifiers, and signal generating means in circuit with ,said gate controlled rectifiers for alternately gating into conductivity said gate controlled rectifiers during successive half cycles .of output from said signal generating means, said capacitance charging'in a polarity during the conductive period of one of said gate controlled rectifiers such'as .to apply reverse voltage thereto to render it nonconductive when the other of said gate controlled rectifiers is initially gated into conductivity, said saturable reactorsbeing so chosen 1 that the after-saturation inductance of said low resist-' .ance winding and said capacitance'form a resonating circuit to provide a commutation interval having a duration to insure the rendering nonconductive of said'one gate controlled rectifier, the product of-the turns of the low' resistance winding, the core area, and core saturation fiux density of the respectivev saturable reactors being chosen to'insure that a reactor goes from one direction to the."

opposite direction of saturation during said interval, said low resistance winding in series arrangement with said other gate controlled rectifier presenting a high impedvance during said interval to prevent said capacitance from discharging into said source and said transformer, the saturable reactor in series arrangement with the nonconductive gate controlled rectifier having its saturation direction switched during the period of conduction of the.

conductive gate controlled rectifier.

j 4. A circuit as defined in claim 3 wherein there are 7 further included first and second diodes connected across said first and second series arrangements respectively.

5. A circuit as'defined .in claim 4 wherein there is further included a current limiting resistance connected between said low power windings.

6. A circuit for converting the output of a DC source to an AC power output comprising first and second saturable reactors, each of said saturable reactor comprising a low resistance winding anda low power winding, first and second inductances, first and second gate controlled senting a low impedance when said first and second gate controlled rectifiers are respectively correspondingly conductive, a third series arrangement of a capacitance and athird; inductance connected between said gate controlled rectifiers andsignal generating means in circuit with said gate controlled rectifiers for alternately gating into conductivity said controlled rectifiers during successive half cycles of output from said signal generating means, said capacitance charging in a polarity during the conductive period of one of said gate controlled rectifiers such as to apply reverse voltage thereto to render it nonconductive when-the other of said gate controlled rectifiers is initially gated into conductivity, said inductances being so chosen as to form a resonating circuit with said capacitor to provide a commutating interval having a duration sufiiciently long to insure the rendering nonconductive of said one gate controlled rectifier the product of the turns of the low resistance winding, the' core area and core saturation flux density of the respective saturable reactors being chosen to insure that a saturable reactor goes from one direction to the opposite direction of saturation during said interval, said low re sistance winding in series arrangement with said other gate'controlled rectifier presenting a high impedance during said interval to prevent said capacitance from discharging into said source and said transformer, the saturable reactor in series arrangement with the nonconducting gate controlled rectifier having its saturation direc tion switched during the period of conduction of the conducting gate controlled rectifier.

7. A circuit as defined in claim 6 wherein the series combination of a first diode and a fourth inductance is connected across said first series arrangement and a second diode and a fifth inductance is connected across said second series arrangement.

8. A circuit as defined in claim 7 wherein'there is further included a current limiting resistance connected between said low power windings.

9. A circuit for'converting the output of a DC source to an AC power output comprising first and second saturable reactors, each of saidsaturable'reactor comprising a low resistance winding and .a low power winding, first v and second diodes, first and second gate controlled rectifiers in first and second series arrangements with said 'fi'rst and second low resistance windings and said first and second diodes respectively, a-transformer connected between said arrangements, said combination of said series arrangements and. said transformer being connected across said source, said first and second saturable reactors presenting a low impedance when said first and second gate'controlled rectifiers are respectively correspondingly conductive, a commutating capacitance connected between said gate controlled rectifiers, and signal generating means in circuit with said gate controlled rectifiers for alternately gating into conductivity said gate controlled rectifiers during successive half cycles of output from said signal generating means, said capacitance chargingin a polarity during the conductive period of oneof said gate controlled rectifiers such as to apply reverse voltage thereto to render it nonconductive when the other of said gate controlled rectifiers is initially gated into conductivity,'said saturable I reactors being so chosen that the after-saturation inductance of said low resistance winding and said capacitance form a resonating circuit to provide a commutation inter-' val having a duration sufficiently long to insure the rendering nonconductive of said one gate controlled rectifier, the product of the turns of the low resistance winding, the core area, and core saturation flux density'of the respective saturable reactors being chosen to insure that a reactor goes from one direction to the opposite direction of saturation during said interval, said low resistance winding in series arrangement with said other gate controlled rectifier presenting a high impedance during said interval to prevent said capacitance from discharging into] said source'and said transformer, the saturable reactor in series arrangement with the nonconducting gate controlled rectifier having its saturation direction switched during the period of conduction of the conducting gate controlled rectifier.

10. A circuit as defined in claim 9 wherein there are further included a third diode connected across said first series arrangement and a fourth diode connectedacrossf said second series arrangement. v

11. A circuit as defined in claim 10 wherein there isfurther included a current limiting resistance connected between said low power windings.

12. A circuit for converting the output of a DC source I,

to an AC power output comprising first and second s aturable reactors, first and second gate controlled rectifiers in'first and second series arrangements with said first and second saturable reactors respectively, a transformer connected between said arrangements, said com- :bination of said series arrangements and said transformer being connected across said source, said first and second saturable reactors presenting a low impedance when said i firsrland second gate controlled rectifiers are respectively v f 1 correspondingly conductive, acommutating capacitance connected between said gate controlled rectifiers, first and second resistances connected across said first and second reactors respectively, and signal generating means in circuit with said gate controlled rectifiers for alternately gating into conductivity said gate controlled rectifiers during successive half cycles of output from said signal generating means, said capacitance charging in a polarity during the conductive period of one of said gate controlled rectifiers such as to apply reverse voltage thereto to I render it nonconductive when the other of said gate con-Iv trolled rectifiers is initially gated into conductivity, said saturable reactors being so chosen that the after-satura tion inductance -of its winding and said capacitance form a resonating circuit to provide a commutation interval having a duration to insure the rendering nonconductive of said one gate controlled rectifier, the product of the turns of the winding, the core area and core saturation I fiux density of the respective saturable reactors being chosen to insure that a saturable reactor goes from one direction to'the opposite direction of saturation during} .said interval, the saturable reactorin series arrangement conducting gate controlled rectifier.

impedance during said interval to prevent said capacitor from discharging into said source and said transformer;

the saturable reactor in 'series'arrangement with the nonconducting gate controlled rebtifierhaving its saturationl direction switched dur ng the period of conduction of the 13. A circuit as defined in claim 12 wherein'there are further included first and second diodes connected across said first and second series arrangements respectively;

14.A circuit for converting the output from a DC source to an AC power output'comprising first and second saturable reactors, each of said reactors comprising a low resistance winding and a low power winding, first and secondgate controlled rectifiers in first and second series arrangements with said first and second low resistance I windings respectively, a transformer connected between said arrangements, said combination of said series arrange I merits and said'transformer being connected across said source,.said first and second saturable reactors presenting a low impedance'whensa'id firstand second gate con trolled rectifiers are respectively correspondingly conducnectedacross said first series arrangement an'da fourth series arrangement comprising .said second low power winding and a second diode connected across said second series arrangement, and signal generating means in circuit with said gate controlled rectifiers for alternately gating into conductivity said=controlled reetifiers during successivehalfcycles of output from said signal generating means, said capacitance charging in a polarity during the conductiveperiod of one of said gate controlled rectifiers such as to apply reverse voltage'thereto to render itnonwith the other'gate controlled rectifier presenting ahigh j capacitance form a resonating circuit to provide a commutation interval havinga duration to insure the rendering nonconductive of said one gate controlled rectifier,

live, a commutating capacitance connected between said .gate controlled rectifiers, a third series arrangement comprising said low power winding and a first diode conconductive when the other of said gate controlled recti- I fiers is initially gated into conductivity, said'saturable reactorsbeing'so chosen that the after saturation of the low resistance and low power winding together with said gate controlled rectifier havingits saturationldirection; it switched during the period of conduction 'of the con connected between said third windings. a

I LEE T.- HIX, Primary Examiner. j SHOOP, Assistant Examiner.

the product of the turns of the low resistance winding, the

corearea, and core saturation flux density of the respective saturable reactorsbeing chosen to insure that a; saturable reactor goes from one direction to the opposite direction of saturation during said interval, said low resistance winding in seriesarrangement with said other gate controlled rectifier presenting a high impedance dur- I ing said interval to prevent said capacitor'from dischar'ging into said source and said transformer, the saturable reactor in series arrangement with the noncondu'cting ducting gate controlled rectifier.

15. Thelcircuit defined in'claim 14 wherein said first and second saturable reactors. further comprise a third winding, each of said third windings being connected to I therespective other windings of said saturable reactors and wherein there is further included a resistance 7 16. The circuit definedin claim'15 wherein first and series arrangements. Y t

17. The circuit defined in claim 14 wherein there are. further included respective resistances connected across References Cited a UNITED STATES PATENTS" I "3,080,534 3/1963 ,Paynter 3,085,190 4/ 1963 Keams al. 

1. A CIRCUIT FOR CONVERTING THE OUTPUT FROM A DC SOURCE TO AN AC POWER OUTPUT CMPRISING A FIRST SERIES ARRANGEMENT OF A FIRT CONTROLLED RECTIFIER AND A FIRST SATURABLE DEVICE CONNECTED ACROSS SAID SOURCE, AND SECOND SERIES ARRANGEMENT OF A SECOND AND COMPLEMENTARY GATE CONTROLLED RECTIFIER AND A SECOND SATURABLE DEVICE CONNECTED ACROSS SAID SOURCE, SAID FIRST AND SECOND SATURABLE DEVICES RESPECTIVELY PRESENTING A LOW IMPEDANCE WHEN SAID FIRST AND SECOND GATE CONTROLLED RECTIFIERS ARE CORRESPONDINGLY RESPECTIVELY CONDUCTIVE, A COMMUNTATING CAPACITANCE CONNECTED BETWEEN SAID GATE CONTROLLED RECTIFIERS, AND SIGNAL GENERATING MEANS IN CIRCUIT WITH SAID GATE CONTROLLED RECTIFIERS FOR ALTERNATELY GATING INTO CONDUCTIVITY SAID GATE CONTROLLED RECTIFIERS DURING SUCCESSIVE HALF CYCLES OF OUTPUT FROM SAID SIGNAL GENERATING MEANS, SAID CAPACITANCE CHARGING IN A POLARITY DURING THE CONDUCTIVE PERIOD OF ONE OF SAID GATE CONTROLLED RECTIFIERS SUCH AS TO APPLY REVERSE VOLTAGE THERETO TO RENDER IT NONCONDUCTIVE WHEN THE OTHER OF SAID GATE CONTROLLED RECTIFIERS IS GATED INTO CONDUCTIVITY, THE SATURABLE DEVICE IN SERIES ARRANGEMENT WITH SAID OTHER GATE CONTROLLED RECTIFER PRESENTING A HIGH IMPEDANCE WHEN SAID OTHER GATE CONTROLLED RECTIFIER IS INITIALLY GATED INTO CONDUCTIVITY. 